Permeable airfoil skin



Feb; 18, 1969 A, L ZE 3,428,278

PERMEABLE AIRFOIL SKIN Filed June 1, 1966 Sheet of 2 INVENTOR ATTYS Feb. 18, 1969 A. GLAZE PERMEABLE AIRFOIL SKIN Sheet Filed June 1, 1966 FIGS FIG 7 E Z A L G Ov WE L & M D R A V ATTY s United States Patent Office 3,428,278 Patented Feb. 18, 1969 3,428,278 PERMEABLE AIRFOIL SKIN Ardelle Glaze, Fort Wayne, Ind., assignor to Fort Wayne Metals, Inc., a corporation of Indiana Continuation-impart of application Ser. No. 499,747, Oct. 21, 1965. This application June 1, 1966, Ser. No. 554,455 US. Cl. 245-8 Claims Int. 'Cl. B21f 27/10; B64c 3/26 ABSTRACT OF THE DISCLOSURE The present invention relates to improvements in woven metal fabrics suitable for use as skin for airfoils or the like. This is a continuation-in-part of my copending application, Ser. No. 499,747, filed Oct. 21, 1965, now Patent No. 3,266,130 granted Aug. 16 1966 which application is itself a continuation-in-part of Patent 3,213,527, granted Oct. 26, 1965.

While airfoils are most commonly recognized as constituting the lift or reaction elements of aircraft, it is of course known that airfoil surfaces are employed in many other structures where reaction is to be obtained from gaseous flow over curved surfaces as, for example, in propellers, turbine blades, jet engine blades, after-burner buckets and the like, and in the present disclosure the term airfoil is to be considered as having the broad connotation which includes reaction surfaces of the aforesaid character.

As applied specifically to the design and operation of aircraft, it is often desirable to provide for the passage of fluid such as air through at least certain specific areas of the skin material of the aircraft, as for example, in sections of the leading edges thereof. The forcing of fluid through the skin material may be desired for several different reasons, one of the more common of which is the attainment of boundary layer control where air is drawn inwardly by suction or blown outwardly in selected areas of the wing surfaces, fuselage surfaces, tail surfaces, nose surfaces and the like so as to improve the lift, drag and other performance characteristics thereof.

Moreover, woven fabric has superior resistance to tear, particularly when laminated, and the use of drawn brazed strands for weaving increases fatigue resistance over comparable sheet material.

Another sitfiation, in which passage of air through certain areas of the skin material of an airfoil is desirable, is for the purpose of producing a de-icing action and in such instances warm air is forced through leading edge surfaces of the wings to break up or melt ice formation.

Still a third instance where such fluid flow through the skin material is desired is in high speed, high altitude flying where severe heating of the surfaces of the aircraft requires the application of a cooling medium. Cooling may now be accomplished by the passage of fluid through the airfoil or aircraft skin materials as part of a process known as transipration cooling. Still other instances where such fluid flow may be advantageously employed are found in jet engine blades, after-burner buckets and other high temperature applications where effective cooling is highly desirable.

In such cases, where a permeable skin material has practical application, attainment of the desired function in a uniform manner requires that the degree of permeability of the skin material be precisely controlled, and since this material is, in the aircraft applications described, in contact with a high velocity air stream, the surface of the permeable material must have optimum smoothness consistent with the permeable character of the material, thereby reducing friction on the skin surface.

Permeable skin material as it is incorporated in the structure of an airfoil is utilized, in many instances, in areas usually covered by sheet metal material, and must therefore possess comparable strength and the capability of being readily secured to the frame of the airfoil. Moreover the exposed surfaces of the skin material must be corrosion and Wear resistant since it must encounter salt water, oils, fuels and particulate matter in the air, and, often at elevated temperatures, e.g., in excess of 650 Fahrenheit.

Now, therefore, it is an objective of the present invention to provide a novel woven metal fabric, capable of lamination, usable as airfoil skin, having a smooth finish, while providing a readily controlled degree of permeability suitable for the accomplishment of the various desired cooling, de-icing, and other functions set forth hereinabove.

Still another object of the present invention is to provide a skin material which may be woven and processed to provide distinct areas of desired permeability, or to provide a permeability gradient of any desired rate of change. It will be understood that the term woven as used herein means the formation, by interlacing, of a fabric with metal wires, whether stranded, as for example, the construction taught by my United States Patent No. 3,213,527, issued Oct. 26, 1965, for Method of Making Permeable Airfoil Skin Material, rounded, flattened, or of any other cross section configuration.

The foregoing and other objects and advantages of the present invention will be apparent from the following detailed description taken conjunction with the appended drawings wherein:

FIGURE 1 is a fragmentary sectional view taken transversely through a woven wire fabric having a series of wires of varying spacing and diameters and showing the same in the condition which it assumes after being woven;

FIGURE 2 is a fragmentary sectional view similar to FIGURE 1, showing the structure after a flattening operation has been performed;

FIGURE 3 is a fragmentary sectional view taken transversely through a woven wire fabric having uniform wire diameters, and in which the spacing between adjacent parallel wires is varied;

FIGURE 4 is a sectional view similar to FIGURE 3, showing the structure after a flattening operation has been performed;

FIGURE 5 is a fragmentary plan view, greatly enlarged, of a woven wire fabric in which variable permeability is attained in the final product by effecting a progressive reduction in wire size, as well as in wire spacing, both as regards the warp and the weft wires;

FIGURE 6 is a schematic representation of an exemplary process of finishing the woven fabric of the present invention;

FIGURE 7 is an elevation of a laminar skin structure of controlled permeability, embodying still another aspect of the invention;

FIGURE 8 is an end view of an exemplary laminar structure wherein the top lamina has been rolled t provide a smooth finish; and

FIGURE 9 is a view showing a combustible or soluble thread interwoven in the fabric, the weave being shown as coarse for purposes of illustration.

While the invention is susceptible of various modifications and alternative constructions, certain illustrative embodiments have been shown in the drawings and will be described below in considerable detail. It will be understood, however, that the absence of a complete detailed discussion of all possible embodiments and variations thereof is not indicative of an intention to limit the invention to the specific forms disclosed. On the contrary, the invention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention as expressed in the appended claims.

The prior applications hereinabove referred to are concerned with an airfoil skin material including a compound woven fabric of a woven wire permeable fabric sheet. The disclosed fabrics are both corrosion resistant and heat reflective, and permeability is variable by varying wire diameter. The use of pressure to effect smoothing of the surface is also disclosed. In the performance of the smoothing operation, the crests (which occur is both the warp and the weft wires) are pressed into a somewhat interlocking relationship with adjacent transversely extending wires, at points of original tangency therewith, thus providing interlocks at each intersection. At the same time, a general flattening of the sheet to a predetermined dimension takes place.

Graduated permeability in the airfoil sheet is attained by providing originally round or other shaped warp and/ or weft wires of diameters or dimensions which vary progressively in one direction so that after the flattening operation, the interstices between the crossed wires will be of a correspondingly gradually diminishing size.

It is evident that permeability, or the capacity of the skin material to pass air or other fluid therethrough is a function of the area of the spaces (interstices) between each of a series of intersecting wires. In accordance with the invention, the degree of permeability maybe increased or decreased by selective placement of the wire strands with respect to one another. Otherwise stated, parallel wires may be positioned from one another by a predetermined amount so that when they are intersected by transverse wires of the weave, controlled spacing results to form the desired area of the interstices between each. In such an application, the strands may be of identical diameter as in FIGURE 3, or varying diameter as taught in my aforementioned application as in FIGURE 1, thus compounding the control over permeability by varying both wire diameter and spacing. Accordingly, by selective use of appropriate diameter wire and strand spacing in the weave, permeability may be precisely controlled within discrete areas of a fabric section while providing a strong airfoil skin capable of resisting heavy frictional and shear loads which would normally be applied to it.

More specifically, in manufacturing the skin material of the present invention, the type, cross section, and dimension of wires to be used for the warp and weft are preselected, it being understood that they be either stranded or solid, and of any suitable shape. After determining the permeability desired for a particular area of the skin, the selected wires are woven, or interlaced, together such as seen in FIGURES l and 5, In FIGURE 1, for

example, a portion of a fabric 10 is shown which comprises warp wires 12 and 'weft, or woof, wires 14. The spacing of the various wires is, in accordance with the invention, variable, as may be seen in FIGURE 5, decreasing from lelt to right as there shown.

Once woven, the resutling fabric 10 is, in keeping with the invention, bonded for the purpose of attaching intersecting wires, thereby securing them in their relative position.

Engagement of intersecting strands of the woven fabric may be accomplished in a number of ways. A particularly practical manner of accomplishing this is the electrical, mechanical, or chemical plating or coating of the individual strands with a material such as silver or copper prior to weaving. Once woven, the fabric is subjected to heat sufficient to melt the plating material, and fusion or bonding is effected at wire intersections.

Another arrangement, suggested by FIGURE 6, contemplates the use of a known electroplating process, represented schematically, and identified as P. The process comprises immersion of the fabric (or individual strand) into a chemical salt bath and placing a source of electrical potential between the fabric and a second conductive metal pole within the bath.

The fabric here shown i woven prior to coating, which is an alternative possibility. The electroplating has the effect of depositing bonding material of a lower melting point at the wire junctures to secure the various wire strands together, thereby securing each strand with respect to every other strand with which it is engaged. It is to be understood that any other suitable brazing or bonding arrangement may be used without departing from the invention. For example, ultrasonic pressure bonding by magnet0stricti011 may be employed.

Once bonded, fabric is then subjected to one, or a series of rolling steps as shown schematically in FIGURE 6'at R and R so as to compress and flatten the wires, bringing about a transverse deformation of the wires at a surface thereof, beyond their elastic linit. The flattened knuckles of the wires give a smooth appearance at least on the surface engaged by the roller, and the thickness thereof is also reduced. It will be appreciated that both surfaces may be rolled with the same result. Where one surface only is to be flattened, on the other hand, a resilient pad is used to engage the opposite surface. Because the application of pressure may, in some instances, fracture or weaken a bonded joint between two intersecting wires, the bonding step may be repeated between rolling operations, as at P A heater of some known type, represented at H, may be employed to bring about a final setting of the bonded intersecting wires.

While rolling is specifically disclosed, it will be appreciated that forging or pressing operations may accomplish the same desirable result.

' The rolling, forging, or pressing process, in addition to providing a smoothing effect, has a predictable effect on the spaces between the wires, thus permitting initial spacing to take into account changes in the spacing between the wires as a result of the rolling process. While intermediate bonding (as at P) of the wires at their juncture inhibits spreading during rolling, nonetheless, some spreading is experienced and may, in the manner disclosed, be controlled and therefore be put to use in developing the finished product.

Selective use of gradually decreasing or increasing diameter wires in both warp and weft accomplishes, as previously taught, a determinable change in the size of the interstices in a diagonal direction. Thus, referring to FIGURE 5, a fabric 30 having warp wires 32 and weft wires 34 is provided, the former decreasing in diameter from right to left, while the latter decreases from top to bottom as illustrated. As a consequence there is a controlled net decrease in the area of the spaces between intersecting wires in the direction of arrow A. This arrangement is merely exemplary of the numerous combinations and permutations which may be employed to obtain a desired permeability gradient over specific areas of a given airfoil skin.

Still another arrangement for providing controlled permeability, in accordance with the invention, is the subjecting of the skin, in rolled and/or unrolled condition, depending upon its intended use, to an electroplating process (such as the type discussed with respect to FIG- URE 6) to bring about a build-up of plated material on the wires, thereby decreasing the space between them. Accordingly, a controlled reduction in permeability is readily achieved. Electroplating processes in particular, being capable of a high degree of control of ion transfer, permit very accurate control of the resultant size of the interstices, and, thus, the permeability of the wire fabric. Further, selected sections of the fabric may be subjected to more or less plating, as desired, so as to permit selective finishing of sections of the same fabric onset. Indeed, specified areas may be completely infiltrated by fusion with plating material or the like such as metal powder or foil so as to permit the use of fasteners through the skin to hold it securely in place.

Still another means of achieving the desired permeability gradient in a woven wire fabric comprises the interweaving in both the warp and weft of the fabric a combustible or dissolva'ble thread. Such an arrangement illustrated in FIGURE 9 wherein warp wires 50 and weft wire 52 are woven into fabric. Interspersed between these wires, and woven as part of the fabric itself, are, e.g., cloth threads 54 which, when subjected to suitable low temperature flame, ignite and burn out the fabric, thereby leaving a predetermined space between adjacent and intersecting wire strands. It will be appreciated that variations in the size of the combustible or dissolvable thread will permit corresponding variation in the porosity of the fabric. It will also be appreciated that the combustible threads may be woven into the fabric in selected areas only to thereby provide discreet areas of predetermined porosity. While a combustible thread is specifically disclosed, it will be appreciated that a thread capable of being dissolved in a suitable non-corrosive chemical will provide the same result.

Where the intended use makes it desirable that the surface finish be highly refiective, but permeability is nonetheless necessary, both characteristics may be achieved, in accordance with the invention, by developing a laminar structure consisting of two or more layers of wire fabric of appropriate mesh bonded together, as contrasted to being interwoven as discussed in the pre viously noted applications.

Referring to FIGURES 7 and 8, the uppermost layer 40 may be of an extremely fine mesh, the wires themselves being stranded or solid. A fabric of about .0015" thickness and having mesh on the order of 200 wires in the warp and 1400 wires in the woof has proven satisfactory, and may be formed of stainless steel or another suitable high temperature alloy. The remaining layers 42 and 44 are preferably of heat dissipating alloy wire cloth and may be of a more coarse weave. Individual layers may be preformed as shown in FIGURE 6. Rolling, in particular, provides a flattening at the wire joints or knuckles which provides excellent surface area for later laminating processes.

Indeed, bonding of the various laminar layers may be facilitated by using the same bonding or electroplating material already present to secure the strands of wire in each of the layers. By induction heating, ultrasonic welding, or in a controlled atmosphere, the bringing together of laminar layers under favorable conditions would activate the already present bonding material with the resultant intra-bonding of the laminae to one another without the addition of more bonding material between them.

Alternatively, additional bonding materials may be used between layers of the laminae. For example, a solder or brazing wire or the like might be interwoven in one or more of the layers so that the application of appropriate heat would cause melting, and consequent bonding when the sheets are pressed together. Wires may also be electroplated before weaving as previously discussed. Laminar sheets formed in this manner may vary in thickness from 0.0036 to 0.020 for many applications, and are exceptionally strong.

All of the laminar layers are bonded together in a fashion which would, in keeping with the present invention, maintain the desired degree of permeability.

According to this aspect of the invention, selective positioning of layers (see FIGURE 7) is provided so that an angle is defined between the longitudinal direction of the warp wires, for example, of the respective layers to determine permeability of the resultant fabric. In the case shown, the warp wires of the illustrated layers define an angle of approximately 30, 40, and respectively, or as in FIGURE 8, they are parallel. The particular alignment used involves a choice based upon the desired degree of permeability, and stress requirements.

It will be seen that the end product is capable of an overall smoothness on its outer surface when a fine mesh layer is used, which can be further rolled for smoothness and controlled permeability brought about by the orientation and configuration of the under layers bonded thereto. The fabric is exceptionally strong and capable of presenting practically any desired surface smoothness to the atmosphere. Furthermore, specific areas can be completely filled so that the fabric may be readily secured in any known manner to wing struts, honeycomb structure, or other bracing forming the superstructure of the airfoil. Moreover, such a laminar stucture may be readily sheared, welded, riveted, and is highly resistant to heat, radiation, fatigue, and the elements generally. As constructed, the fabric may appear absolutely smooth to the extent that light will not pass through it. Nonetheless, because of the weave characteristics, the fabric will have microscopic spaces between wires which render a desired. permeability gradient capable of permitting the passage of gases through the surface for cooling purposes, ice removal, or other purposes, as hereinbefore mentioned. The convolute apertures to each interstice or channel of opening provide easy back wash for removing clogging dust particles.

I claim:

1. A permeable fabric material adapted for use as part of an airfoil comprising a woven stainless steel wire fabric sheet having a first series of spaced apart generally parallel wires defining the warp of said material and a second series of similarly spaced apart generally parallel wires defining the weft of said material, said warp and weft being disposed in interlacing relationshi the size of certain ones of the wires in each of said series decreasing progressively, so that the interstices between adjacent and intersecting wires vary progressively in size and thereby provide a material of locally variable permeability.

2. A material as set forth in claim 1 wherein the spacing between adjacent wires in one of said series is varied.

3. A material as set forth in claim 2. wherein the spacing between adjacent wires in each one of said series is varied.

4. A permeable fabric material adapted for use as part of an airfoil comprising a woven wire fabric sheet having a first series of spaced apart generally parallel wires defining the warp of said material and a second series of spaced apart generally parallel wires defining the weft of said material disposed in interlacing relationship, the spacing between adjacent pairs of parallel wires in each of said series being varied in the direction of extent of the wires of the other series so that interstices between adjacent and intersecting wire portions vary in size and in said direction of said spacing change and thereby provide a material of locally variable permeability.

5. A material as set forth in claim 4 wherein the size of certain ones of the wires in one of said series decrease progressively.

References Cited UNITED STATES PATENTS 9/1891 Riggs 2458 Reynolds 245-8 De Laski 39425 Mitchell 2458 Green 139-425 Brown 245-8 Roberts 29-1635 RICHARD J. HERBST, Primary Examiner. 

